The schistosome egg plays central roles in the life history of the worms and in the pathophysiology of schistosomiasis, yet relatively little is known about the cell biology and biochemistry of egg formation by the female. Production of the vitelline cell, the source of eggshell material, occupies the bulk of the female's metabolic and biosynthetic output, and offers an ideal target for specific intervention by drugs. This proposal is the beginning of a long term study to elucidate the processes of vitellogenesis and eggshell formation in Schistosoma mansoni. Initial efforts will focus on the following topics: Cytochemical characterization of the lysosomal system of the vitelline cell. Cytochemical localization of polyphenol oxidase and peroxidase in the vitelline cell and vitelline granule. Isolation, and structural and functional characterization of the vitelline granule. Electron microscopy, ultrastructural cytochemistry, cell fractionation, enzyme analysis, and amino acid and carbohydrate analysis will be the primary methods applied. The results of the above studies can be applied 1) To gain a better understanding of the sequence of events and regulation of eggshell formation, and 2) To search for and evaluate drugs and other agents which target on vitellogenesis and eggshell formation.